[Asterisk-Users] best protocol/codec for dialup

[snacktime]

What would be a good combination to use on dialup connections?  I know
iax is better than SIP, but I dont' know much of anything about the
various codecs.  Also, how well would an iax or sip solution work
compared to skype as far as voice quality?

If it helps, here is what I'm trying to do.  We know about 30
different families in one area in Russia that have relatives here in
the US.   What I want to do is put in an * server with a couple of
pstn lines in Russia so that all of them have the ability to call the
US by making a local call.    Most of the time these familes can't
afford to call their relatives in the US, and internet access is
fairly expensive as well, although some of them do have it.

Chris